A thrust reverser is a mechanical device that is deployed to redirect exhaust flow from one of an aircraft's gas turbine engines, typically just subsequent to the aircraft landing. Thrust reversers are normally deployed during the landing sequence, after the nose wheel has touched down (usually called the "rollout"). Thrust reversers can greatly reduce the length of runway necessary to bring the aircraft to taxi speed, and they are also used when adverse weather conditions, such as ice on the runway, may cause the aircraft's brakes to be ineffective.
There are two basic types of thrust reversers, the "pre-exit", and the "postexit." Schematics of both of these designs are shown in FIGS. 1A-3B. The post-exit reverser, as illustrated in FIGS. 1A and 1B, is seen to redirect the engine exhaust jet after it leaves the engine's tailpipe. Pre-exit reversers, as illustrated in FIGS..2A, 2B, 3A and 3B, turn the flow in the exhaust tailpipe before it is expanded to ambient. Thus, the pre-exit reverser generates lower forces on the blocker doors. In the actuated-mode, the pre-exit reverser is aerodynamically cleaner, and could be actuated in flight with minimal drag effects, e.g., as a result of inadvertent actuation.
Many older jet engines, such as the Spey.RTM. 511-8 turbofan engines manufactured by Rolls Royce Ltd., have post-exit thrust reversers, as shown in FIGS. 1A and 1B. There, the engine exhaust jet exits the engine nozzle, hits the reverser buckets and is redirected in the forward direction, as indicated by the directional flow arrows. The reverser is used to redirect about 12,000 pounds of thrust generated from the engine with a jet velocity of approximately 1900 ft/sec. The loads on the buckets, and the linkages actuating the buckets, are extremely large. Also, the effectiveness of the reverser is limited to the ability of the buckets by themselves to turn the flow. Post-exit reversers of this type tend to be much less effective than pre-exit reversers. Also, in-flight actuation of such bucket reversers can cause catastrophic drag and jet forces on the aircraft.
Although these older, post-exit thrust reverser jet engines are functional, the engines produce excessive amounts of noise. This is because the engines have low bypass ratios and extremely high jet velocities. In low bypass ratio turbofan engines, most of the energy from the burnt fuel is used to raise the pressure and temperature of the engine flow. Engine and fan streams are usually mixed and exhausted through a common nozzle. This results in high nozzle pressure ratios, high jet velocities, and high levels of noise. In fact, planes carrying these engines, such as the common business-class Gulfstream.RTM. GII, GIIB, and GIII, typically violate the federal "stage three" jet engine noise requirements, which are the latest United States government standards imposed to reduce noise pollution around major urban areas.
As a result, a Two Stage Mixer/Ejector Concept (TSMEC.TM.) noise suppressor was originally formulated, analyzed and proposed as a possible solution to the Gulfstream.RTM. GII/GIIB/GIII aircraft jet noise problem. The TSMEC.TM. noise suppressor is set forth in U.S. Pat. No. 5,761,900 to Presz, Jr.
Basically, the TSMEC.TM. noise suppressor comprises a lobed ejector shroud coupled to a lobed mixer. Engine exhaust passes out the engine proper, through the lobed mixer, and into the ejector shroud. At the same time, cooler, lower velocity, ambient air outside the engine passes over the lobed mixer to enter the ejector shroud via spaces between the shroud and mixer. The lobed mixer causes the ambient air to quickly mix with the engine exhaust, creating a uniform flow by the time the combined gasses exit the ejector shroud, and, furthermore, cooling and slowing the engine exhaust. This lowers the engine's noise output.
An improved version of the TSMEC.TM. noise suppressor, called an Alternating Lobed Mixer/Ejector Concept (ALMEC.TM.) suppressor, is described in U.S. Pat. No. 5,884,772 to Presz, Jr. et al. ("the '772 patent"), the entirety of which is hereby incorporated by reference. The ALMEC.TM. suppressor has alternating, deep penetrating lobes that provide significantly larger jet noise reduction than the original TSMEC.TM. design.
FIGS. 10-12 in the '772 patent show schematics of the various ALMEC.TM. suppressor components. Like the TSMEC.TM. suppressor, the ALMEC.TM. noise suppressor mixes cool ambient air with the hot, high velocity engine flow before it leaves the exhaust system. In this manner, the resulting exhaust jet is at a much lower velocity and temperature. The lower jet velocities provide the noise reduction needed to satisfy federal stage three requirements.
The ALMEC.TM. suppressor has two major components: the mixer nozzle and the ejector shroud. The mixer nozzle has ten lobes designed to efficiently and rapidly mix the engine flow with ejector secondary air. Five of the lobes are shallow; and they are designed identically to the TSMEC.TM. nozzle lobes. The other five lobes are much longer; and they are designed to penetrate deeply into the hot engine jet core. The shallow and deep lobes alternate around the circumference of the nozzle. The alternating lobes set up separate axial vorticity patterns that interact with each other to enhance mixing and further reduce noise.
The TSMEC.TM. and ALMEC.TM. noise suppressors are available from the common assignee of this application and the above mentioned patents, Stage III Technologies, L.C. of Las Vegas, Nev.
As should be appreciated, both the TSMEC.TM. and the ALMEC.TM. noise suppressors need to be attached to the exit end of a jet engine to function. Therefore, one major problem associated with outfitting the Gulfstream.RTM. GII, GIIB, and GIII (and similar) aircraft with these noise suppressors is that the noise suppressor assemblies would have to be affixed to the engines in roughly the same spaces occupied by the engines' post-exit thrust reversers. Of course, this is impossible.
Moreover, even if it were mechanically possible to use the existing, post-exit thrust reversers with the ALMEC.TM. or TSMEC.TM. noise suppressors, the post-exit reversers would be aerodynamically compatible with neither. As described above, both noise suppressors work by entrainment, sucking ambient air (that flows over the engine nacelle after body) into the ejector shroud. The mixer nozzle lobes mix this ambient air with the higher velocity engine exhaust to generate a lower velocity, quieter exhaust jet. With a post-exit thrust reverser, the flow disturbances caused by the stowed buckets could significantly affect the nearby ambient flow and consequently hinder suppressor performance. More specifically, the current engine nacelle after body closes at an angle near fifteen degrees. This means that the flow boundary layer on the nacelle after body is very close to separating (separation means the flow leaves the after body and nozzle lobe surface). In fact, any surface disturbance, such as that caused by the bucket doors, or even exposed cascade vanes, could cause the after body flow to separate. Such flow separation would cause high losses, poor mixing, and less flow to enter the ejector shroud. The net result would make the ALMEC.TM. and TSMEC.TM. suppressors less effective.
Because post-exit thrust reversers are not compatible with the ALMEC.TM. suppressors (or other, similar-type noise suppressors), a pre-exit thrust reverser must be used instead. While several such reversers are available, as described below, they were not found to be advantageous for use with mixer/ejector noise suppressors like the ALMEC.TM.. More specifically, existing pre-exit thrust reversers are unnecessarily mechanically complex, are still prone to accidental deployment, are not aerodynamically compatible with mixer/ejector noise suppressors, and would require modifications to an airplane's hydraulic or instrumentation systems.
For example, U.S. Pat. No. 4,790,495 to Greathouse et al. discloses a cascade thrust reverser with a pair of internal blocker doors deployable for redirecting engine thrust through a pair of cascades or louvers. Neither doors for covering the cascades from the outside, nor a mechanism for attaching or closing such doors, are provided. The cascades remain open to the air flow over the engine nacelle at all times. This would greatly reduce the effectiveness of a mixer/ejector noise suppressor attached to such an engine. Moreover, the design in Greathouse et al. requires the use of latching solenoids and associated electric control circuitry, requiring extensive modifications to the airplane's existing controls.
Additionally, U.S. Pat. No. 3,734,411 to Wolf et al discloses another cascade thrust reverser. There, numerous components of the reverser mechanism interfere with the exhaust flow traveling through the tailpipe. For example, a plurality of reverser mechanism linkage arms lie internal to (or at least exposed to) the tailpipe bore, which is also apparently traversed by a shaft used to support the blocker doors. Although this would be acceptable for regular, noisy jet engines, it would significantly interfere with the proper functioning of a mixer/ejector noise suppressor, like TSMEC.TM. or ALMEC.TM..
U.S. Pat. No. 3,616,648 to Weise also discloses a cascade thrust reverser. As with Wolf et al, some of the reverser's components lie exposed or internal to the tailpipe bore. Also, the entire rear portion of the nacelle, in the form of an annular cowl supporting the cascades and blocker door assembly, must be moved aft to actuate the thrust reverser. This arrangement is somewhat mechanically precarious. The cowling would likely be unable to physically support a mixer/ejector noise suppressor attached to it.
Finally, U.S. Pat. No. 5,598,701 to Newton discloses a "door-type" thrust reverser (see FIGS. 3A and 3B). There, aft ends of the blocker doors and external doors are supported by a frangible coupling designed to break upon accidental deployment during flight. In this design, blocker door actuation arm tracks are open to the tailpipe bore, and there is no place to attach a noise suppressor (note that extending the outer nacelle housing further aft could potentially interfere with the safety mechanism).
Accordingly, it is a primary object of the present invention to provide a unique, pre-exit cascade thrust reverser compatible for use with a mixer/ejector jet engine noise suppressor.
A more specific object is to provide a pre-exit thrust reverser that includes a safety mechanism that prevents inadvertent deployment of the thrust reverser at any times except subsequent landing.
Yet another object of the present invention is to provide a unique thrust reverser, commensurate with the above-listed objects, that is directly compatible with a jet airplane's existing hydraulic and instrumentation system, such that no "upstream" modifications are required.
Yet another object of the present invention is to provide a thrust reverser that is as light or lighter than existing thrust reversers, thereby ensuring no flight performance penalties.
Still another object of the present invention is to provide a thrust reverser that is specifically aerodynamically compatible with the patented ALMEC.TM. noise suppressor.